1. Field of the Invention
This invention relates to improvements in methods of measuring light transmission losses of optical materials, and more particularly of optical fibers.
2. Description of the Prior Art
Light transmission losses of optical fibers have been measured by methods such as that shown in FIG. 1. In said drawing, light from a lamp 36 is projected into an optical fiber 35 from one end surface 43, is projected out of the other end surface 44, is condensed by an integrating sphere 37, and is converted to an electric quantity by a photoelectric converting element 40, the electric quantity is amplified by an amplifier 41 and its output of amplifier is read out on an indicator 42. This value is denoted by E.sub.1. Then the optical fiber is cut in a position 45 separated from the end surface 44 by a length L measured along the axis of the optical fiber 35. Then the new end surface 45 is fixed in the same position as the end surface 44 by a holder 39 and the indicated value of the indicator 42 is read out. This value is denoted by E.sub.2.
The light transmission loss (absorption coefficient) can be determined from E.sub.1 and E.sub.2 by applying formula (1), having the form of the Lambert-Beer's law: EQU I.sub.1 =I.sub.2 exp(-KL) (1)
where
I.sub.1 :Intensity of the light at the end surface 44. PA0 I.sub.2 :Intensity of the light at the end surface 45. PA0 K:Light transmission loss (absorption coefficient). PA0 L:Length of the cut optical fiber. PA0 .rho..sub.1 :Reflection coefficient of the end surface 44. PA0 .rho..sub.2 : Reflection coefficient of the end surface 45.
I.sub.1 and I.sub.2 are related respectively to E.sub.1 and E.sub.2 by the following formulas: EQU E.sub.1 =(1-.rho..sub.1)I.sub.1 ( 2) EQU E.sub.2 =(1-.rho..sub.2)I.sub.2 ( 3)
where
When formulas (2) and (3) are substituted in formula (1), formula (4) is obtained: EQU K=1/L{ln(E.sub.2 /E.sub.1)+ln (1-.rho..sub.1)/(1-.rho..sub.2)}(4)
If the end surfaces 44 and 45 are cut and/or finished so that .rho..sub.1 and .rho..sub.2 are equal to each other, the light transmission loss may be determined from the following formula (5): EQU K=1/Lln(E.sub.2 /E.sub.1) (5)
Such a conventional method has demerits, in that the cut optical material cannot be used as a product, hence the method cannot be used to test all the products, in that it is not easy to cut or grind and finish the material so that the reflection coefficient of the cut surfaces are equal to each other, and in that the measurement requires a long time.